1. Field of the Invention
The present invention relates to a branch pipe liner with which an aged branch pipe is internally lined, and also to a pipe lining method in which the inventive branch pipe liner and a main pipe liner are used.
2. Description of the Prior Art
When an underground main pipe, such as sewer pipes, becomes defective or too old to perform properly, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. Typically, the method is disclosed by Japanese Provisional Patent Publication (Kokai) No. 60-242038.
According to this publication, this method of pipe repair comprises inserting a sufficiently long tubular flexible liner bag into the pipe to be repaired by means of a pressurized fluid, like air and water. The tubular liner bag is made of a flexible resin-absorbent material layer impregnated with a thermosetting liquid resin, and has the outer surface covered with an impermeable plastic film.
More particularly, according to the publication, the tubular flexible liner bag is closed at one end and open at the other; the tubular flexible liner bag is first flattened. Then, the open end of the tubular liner bag is made to gape wide and hooked (anchored) at the end of the defective or old pipe in a manner such that the wide-opened end of the liner bag completely and fixedly covers and closes the pipe end; a portion of the liner bag in the vicinity of the pipe end is pushed into the pipe so as to create an annular pocket; then, the pressurized fluid is applied to the annular pocket of the tubular liner bag such that the fluid urges the tubular liner bag to enter the pipe. Since one end of the tubular liner bag is hooked at the end of the pipe, it remains there while the rest of the flexible liner bag is turned inside out or evaginated under fluid pressure as it proceeds deeper in the pipe. (Hereinafter, this manner of insertion shall be called "everting".) When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the everted tubular liner bag is pressed against the inner wall of the pipe by the said pressurized fluid or by an inflatable pressure bag, and the tubular flexible liner bag is hardened as the thermosetting liquid resin impregnated through the thickness of the liner bag is heated, which is effected by heating the fluid filling the tubular liner bag by means of a hot steam, etc. Thereafter the closed end of the liner bag is cut off. It is thus possible to line the inside wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
This pipe lining method is similarly applicable to a branch pipe which is in fluid communication with a main pipe such as sewer pipes. Some of the present inventors formerly proposed in a patent application a branch pipe lining method wherein a branch pipe is internally lined with a branch pipe liner bag having a collar-like flange at its open end. More particularly, according to this prior art method, the branch pipe liner bag is positioned in the main pipe and the collar of the branch pipe liner bag is fitted closely on the margin of the opening of the hole defined by the branch pipe; then, the branch pipe liner bag is everted into the branch pipe under fluid pressure so that the liner bag goes up toward the surface of the earth from the main pipe; and when the eversion is completed and the liner bag is closely pressed against the inner face of the branch pipe, the hardenable liquid resin impregnated through the branch pipe liner bag is hardened by heating or some other procedure.
After the branch pipe is internally lined by this branch pipe lining method, the main pipe is lined with a main pipe liner by the conventional pipe lining method as described above. However, this main pipe liner closes the hole by which the branch pipe opens into the main pipe, and, thus, it is necessary to make a hole through the main pipe liner to restore the communication between the main pipe and the branch pipe.
If the inner diameter of the main pipe is smaller than 800 mm, a man cannot enter the main pipe and it is necessary to use a boring robot with a cutter, which is introduced in the main pipe and remote-controlled from the ground to wield the cutter so as to make a hole through that portion of the main pipe liner which closes the branch pipe.
The Problems the Invention Seeks to Solve
However, it requires a dexterity to properly control the boring robot in the operation of making a hole through the main pipe liner, and when the operator is not very careful, the robot's cutter is liable to attack the collar and other unintended portions of the branch pipe liner. When such inadvertent attacks cause breaks, the ground water would penetrate through them into the pipes to cause problems. In certain special cases wherein the connection of the branch pipes to the main pipe is of such configuration that renders the hole making operation difficult, it was inevitable to cause damages on the branch pipe liner by the cutter.
It was, therefore, conceived to protect that portion of the inner face of the branch pipe liner which is adjacent to the collar with a protective member after the branch pipe lining operation.
However, that portion of the main pipe liner which is to be cut off (that is, the portion which closes the branch pipe opening) is curved to fit the curvature of the inner wall of the main pipe, so that the preset length of the stroke of the cutter of the boring robot required to penetrate through the liner varies depending on the inner diameter of the main pipe and that of the branch pipe; furthermore, the required stroke length is also dependent on the boring point along the circumference of the branch pipe opening; consequently, the stroke length has to be set to a maximum required value so that the amount of the thrust of the cutter into the branch pipe liner tends to be large. To cope with this, it was sometimes necessary to protect the inner face of the branch pipe liner with a protective member having a height of no less than 20 mm or even 100 mm, and it was not an easy task to push such a longish protective member into the branch pipe.
Since the protective member is made of a rigid material such as metal, it is not resilient, and, as shown in FIG. 12, a branch pipe (111) is often connected to the main pipe (110) not orthogonally, but at an angle .theta., e.g. 45.degree. or 60.degree., or a branch pipe (211) is connected to the main pipe (210) via an elbow (230) of an angle 45.degree., 60.degree. or 90.degree., as shown in FIG. 13; all of these facts tend to render it virtually impossible to properly insert a lengthy protective member into a branch pipe liner.
The present invention was made in view of the above problem and others, and it is, therefore, an object of the invention to provide a new branch pipe liner which is not liable to be damaged by the robot cutter irrespective of the inner diameters of the main pipe and the branch pipe or of the configuration by which the branch pipe is connected to the main pipe; also it is another object of the invention to provide a new method for lining an underground pipe by which it is possible to conduct the boring operation in the main pipe without damaging the branch pipe liner.